The present invention relates to a valve for controlling flow of hydraulic fluid. Specifically, the valve is a rotary valve used to control the flow of hydraulic fluid from a pump to a power steering motor.
A known power steering control valve for controlling flow of hydraulic fluid from a fixed displacement pump to a power steering motor includes a valve sleeve having a generally cylindrical bore therein and a generally cylindrical valve core rotatably mounted therein. Each of the core and sleeve has a plurality of lands and grooves that cooperate to regulate fluid pressure within the valve and control flow from the pump to the power steering motor.
When the spool and sleeve are in a neutral position, fluid is communicated generally equally to opposite chambers of the power steering motor. When the core and sleeve are relatively rotated from the neutral position, fluid flow is variably restricted. Restriction of the fluid flow causes pressurized fluid to be delivered to one of the chambers of the power steering motor to cause motor actuation.
The restriction is provided by the cooperation of lands on the core and sleeve which define flow orifices of variable size. Relative rotation between the core and the sleeve varies the size of the flow orifices. Upon relative rotation from the neutral position to a displaced position, certain pairs of lands on the core and sleeve radially overlap to restrict the associated flow orifice to only the size of a gap between end face surfaces of the respective pairs of lands. Due to a high volume of hydraulic fluid flow from the pump and pressure changes (drops), noise is generated. The noise includes noise due to cavitation of hydraulic fluid flowing through the flow gaps.